1. Field of the Invention
The present invention relates to an image forming method and an image forming apparatus, and more particularly, to an image forming apparatus and an image forming method whereby an image is formed on a recording medium by using an aggregating treatment liquid and an ink.
2. Description of the Related Art
In general, an inkjet recording apparatus comprises an inkjet head in which a plurality of nozzles are formed, and forms an image on a recording medium by ejecting ink droplets respectively from the nozzles onto a recording medium; such apparatuses are used widely due to their excellent low-noise operation, low running costs, and their ability to record images of high quality onto recording media of many different types.
However, when ink droplets are ejected onto a permeable recording medium which has ink receiving properties, then if droplets are ejected continuously to form adjacent dots which are mutually overlapping, the liquid ink droplets on the recording medium combine together due to surface tension, giving rise to bleeding (landing interference) which prevents the formation of desired dots. In the case of dots of the same color, the dots shape is disturbed and in the case of dots of different colors, an additional problem of color mixing occurs.
In order to suppress bleeding as described above, Japanese Patent Application Publication No. 2004-10633 discloses technology in which one of an aggregating treatment liquid (liquid component) and an ink is made acidic, the other is made alkaline, and the pigment aggregating properties on the surface of the paper are controlled so as to effectively improve the optical density, bleeding (temporal bleeding) and drying time.
Furthermore, Japanese Patent Application Publication No. 11-188858 discloses a recording method which enables high-speed recording without the occurrence of bleeding, by depositing a powder layer (water-soluble resin layer) which generates swelling, viscosity increase and separation by reaction with the ink.
However, in the method described in Japanese Patent Application Publication No. 2004-10633, when droplets of ink are ejected after depositing an aggregating treatment liquid onto a medium of low permeability, for instance, a non-permeable medium such as a plastic sheet, or coated paper, the coloring material which has landed and aggregated moves rather than remaining in the desired position. As a result of this, a new problem arises in that the output image is greatly disturbed in comparison with the desired image.
Furthermore, the following issues arise in the case of the method in Japanese Patent Application Publication No. 11-188858. (1) Since the coloring material in the ink is not aggregated actively, then when ink droplets are ejected at a fast rate of 10 kHz or above, the swelling and viscosity raising actions do not occur quickly enough and the landing interference described above still occurs. (2) Since the transferred image forming layer swells as the ink solvent is absorbed, then the thickness of the image portion increases, giving rise to a problems of the “pile height”. If the image thickness becomes large, then not only is there a problem of image quality due to the change in appearance at the boundaries between a printed region and a non-printed region, there is also a problem in that a step difference will be noticeable when these boundaries portions are touched. (3) Since the ink solvent is absorbed in the transferred image forming layer, this ink solvent bleeds out onto the surface of the paper after transfer and gives rise to deformation of the paper (so-called “cockling”). (4) Since an intermediate transfer body is used, the system is complex. When the final image is formed on the recording medium (paper) while still containing ink solvent, problems (2) and (3) described above both can occur.